Ternary and quaternary fission

In a systematic survey of ternary fission induced by thermal neutrons at the Lohengrin spectrometer of the ILL/Grenoble, the target nucleus249Cf has recently been added to the list of actinides under study. Special emphasis was put on the search for the heaviest ternary particles. At the limit of detection (some 10−9 per fission), the heaviest isotopes observed for249Cf(nth,f) are37Si and37S. Another rare process in low energy fission is quaternary fission. Here two light charged particles accompany the main fragments. The reaction233 U(n,f) has been studied at a cold neutron beam of the ILL. Two processess have to be disentangled: simultaneous and sequential quaternary fission. In the simultaneous decay the most probable combination of particles is (α + α) with a yield of ∼10−7/fission.